In a hologram screen for reproducing an image based on an output light obtained by scattering and diffusing an image light from an image projector, when a white light (image light) is projected on the hologram screen; and when a distance between two points at optional two points A and B on a surface of the hologram screen is given by 20 cm or less, and a value of the CIE 1976 chromaticity coordinate (u', v') at the point A is given by (u'A, v'A) and the value of the CIE 1976 chromaticity coordinate (u', v') at the point B is given by (u'B, v'B); the output light perpendicularly from the surface of the hologram screen has a color distribution in which a color difference Δu'v' between two points A and B is derived from the following formula (1) and given by 0.06 or less, where, the formula (1) is expressed by,
Further, the output light, which is output to a viewpoint defined by the following formula (2) from the surface of the hologram screen, has the color distribution in which a color difference Δu'v' between two points A and B is derived from the above formula (1) and given by 0.01 or less, where, the formula (2) is expressed by,
in the formula (2), L is a distance between the viewpoint and a center of the hologram screen, and H is a length of the hologram screen in the direction of the height.
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1. A hologram screen for reproducing an image based on an output light obtained by scattering and diffusing and image light from an image projector, characterized in that;
said hologram screen present an optical spectrum whose bandwidth is 100 nm or more; and said hologram screen is comprised of a hologram element which is made by forming an interference fringe on a photosensitive material, said interference fringe being formed by irradiating an object light and a reference light onto said light sensitive material, said object light being made of a light diffused by a light diffusion body having a large diffusion angle and said reference light being made of a non-diffused light, where said light diffusion angle of the light diffusion body is set to 9 degrees or more such that the half bandwidth of said optical spectrum of the hologram screen is 100 nm or more.
6. A hologram screen for reproducing an image based on an output light obtained by scattering and diffusing an image light from an image projector, characterized in that;
said hologram screen present an optical spectrum whose bandwidth is 100 nm or more; and said hologram screen is comprised of a hologram element which is made by forming an interference fringe on a photosensitive material, said interference fringe being formed by irradiating object lights and reference lights onto said light sensitive material, said object lights being made of diffused lights which are obtained irradiating a plurality of lights incident onto a light diffusion body at different angles and said reference lights being made of non-diffused lights, where said light diffusion angle of the light diffusion body is set to 9 degrees or more such that the half bandwidth of said optical spectrum of the hologram screen is 100 nm or more.
2. A hologram screen as claimed in
3. A hologram screen as claimed in
4. A hologram screen as claimed in
5. A hologram screen as claimed in
7. A hologram screen as claimed in
8. A hologram screen as claimed in
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This is a division of U.S. patent application Ser. No. 09/348,009, filed Jul. 6, 1999 now U.S. Pat. No. 6,421,147.
1. Field of the Invention
The present invention relates to a hologram screen and a method of producing the same. In particular, a first aspect of the present invention relates to a hologram screen for reproducing an image based on an output light obtained by scattering and diffusing an image light which is input from an image projector, and a producing method of the same; a second aspect of the present invention relates to a producing method of a hologram element which can be used as a display apparatus for displaying the image, such as a still image and an animation, by irradiating the image light thereto; a third aspect of the present invention relates to a hologram screen and a producing method of the same; and a fourth aspect of the present invention relates to a hologram screen for reproducing an image based on an output light obtained by scattering and diffusing an image light.
2. Description of the Related Art
A hologram screen, which is formed by a hologram element and a transparent glass, has been widely known in the field of image projecting techniques. A hologram element is of basically two types, i.e., a light-transmitting type and a light-reflecting type and the position of an observer who observes the hologram screen is different in each type.
As representative problems to be solved in a conventional hologram screen, there are the quality of the image, such as unevenness of color and brightness on the hologram screen, cloudiness and a partial non-transparent state on the hologram screen, and the difficulty of preparing very large hologram screen. These problems will be explained in detail with reference to the attached drawings described below.
The first object of the present invention is to provide a hologram screen, which has no unevenness of color on the reproduced image, and a method of producing the screen
The second object of the present invention is to provide a method of producing a hologram screen in which an observer can observe a uniformly bright image without change of brightness and color to a broad extent on the hologram screen.
The third object of the present invention is to provide a hologram screen, which has good reappearance of the reproduced image on the hologram screen and which can realize low cost and easy production of the hologram screen, and a method of producing the screen.
The fourth object of the present invention is to provide a hologram screen which has good transparency and no cloudy state so that the observer clearly and easily observe the back of the hologram screen.
In accordance with a first aspect of the present invention, there is provided a hologram screen, and a method of producing the same, for reproducing an image based on an output light obtained by scattering and diffusing an image light from an image projector, characterized in that; when a white light is used as the image light and projected on the hologram screen; and when a distance between two points at optional two points A and B on a surface of the hologram screen is given by 20 cm or less, and a value of the CIE 1976 chromaticity coordinate (u', v') at the point A is given by (u'A, v'A) and the value of the CIE 1976 chromaticity coordinate (u', v') at the point B is given by (u'B, v'B); the output light, which is output perpendicularly from the surface of the hologram screen, has a color distribution in which a color difference Δu'v' between two points A and B is derived from the following formula (1) and given by 0.06 or less, where, the formula (1) is expressed by,
Further, the output light, which is output to a viewpoint defined by the following formula (2) from the surface of the hologram screen, has a color distribution in which a color difference Δu'v' between two points A and B is derived from the above formula (1) and given by 0.01 or less, where, the formula (2) is expressed by,
in the formula (2), L is a distance between the viewpoint and a center of the hologram screen, and H is a length of the hologram screen at the direction of the height.
In a preferred embodiment, a spectral characteristic of the output light, which is output perpendicularly from the surface of the hologram screen, has a characteristic in which either a difference between peak wavelengths at the whole of the surface of the hologram screen is given by 120 nm or less, or a difference between half bandwidth is given by 100 nm or less.
In another preferred embodiment, when producing the hologram screen defined in claim 1 or 2 by irradiating the object light and the reference light onto a photosensitive material and by exposing the photosensitive material, the photosensitive material has a thickness distribution which is inclined to an incident direction of the reference light.
In still another preferred embodiment, when an incident angle of the reference light to the photosensitive material becomes larger, the thickness distribution of the photosensitive material becomes thicker.
In still another preferred embodiment, when the thickness at a center of the photosensitive material is T0, and when thickness difference of both ends of the photosensitive material is ΔT, the following relationship, i.e., ΔT≦0.5T0, is defined.
In still another preferred embodiment, the thickness distribution of the photosensitive material is defined by the following formula (3), i.e.,
where, T is a thickness at an optional point on the photosensitive material, T0 is a thickness at the center of the photosensitive material, R is an incident distance of the reference light at the optional point on the photosensitive material, R0 is the incident distance of the reference light at the center on the photosensitive material, θ0 is an incident angle of the reference light at the center of the photosensitive material, and "b" is a coefficient determined by the thickness of the photosensitive material and given by 0<b<1.
In still another preferred embodiment, when producing the hologram screen defined in claim 1 or 2 by irradiating the object light and the reference light onto a photosensitive material and by exposing the photosensitive material, ultraviolet light is previously irradiated onto the photosensitive material so as to have an energy distribution which is inclined to an incident direction of the reference light.
In still another preferred embodiment, the energy distribution of the ultraviolet is given by the following formula (4), i.e.,
where, R is the incident distance of the reference light at the optional point on the photosensitive material, Euv is an amount of energy of the ultraviolet irradiated to the optional point on the photosensitive material, R0 is the incident distance of the reference light at the center of the photosensitive material, and E0 is the amount of energy of the ultraviolet irradiated to the center of the photosensitive material.
In still another preferred embodiment, when producing the hologram screen defined in claim 1 or 2 by irradiating the object light and the reference light onto a photosensitive material and by exposing the photosensitive material, an incident distance of the reference light at an optional point of the reference light is shorter than an incident distance of an image light which is irradiated from an image projector when reproducing the image on the hologram screen.
In still another preferred embodiment, when producing the hologram screen defined in claim 1 or 2 by irradiating the object light and the reference light onto a photosensitive material and by exposing the photosensitive material, an intensity ratio of the reference light and the object light is defined by a relationship of IR/IO≦10, on the whole of the surface of the photosensitive material, where, IR is the intensity of the reference light, and IO is the intensity of the object light.
In accordance with a second aspect of the present invention, there is provided a method for producing a hologram screen formed by interfering of a reference light and an object light transmitted through a light diffusion body, and by recording the light diffusion body on a photosensitive material, characterized in that; a mirror is arranged approximately perpendicular to the light diffusion body; the photosensitive material and the light diffusion body are rotated by the same angle θ around an axis which is intersected perpendicularly to a center of the photosensitive material and used as a rotational center; and a polarized direction of a laser light is defined by either P-polarization or S-polarization which is inclined by the angle in the range of θ-5 to θ+5.
In accordance with a third aspect of the present invention, there is provided a hologram screen for reproducing an image based on an output light obtained by scattering and diffusing an image light from an image projector, characterized in that; a half bandwidth of a spectral characteristic of the hologram screen is given by 100 nm or more; a diffusion light which is obtained by a light diffusion body having a large light diffusion angle is used as an object light; a non-diffusion light is used as a reference light; and the object light and the reference light are irradiated on a photosensitive material in order to form an interference fringe so that a hologram element is produced.
In a preferred embodiment, the light diffusion angle of the hologram screen is defined by an angle in which the light diffusion angle of the hologram screen is 10°C or more.
In another preferred embodiment, a half bandwidth of a spectral characteristic of the hologram screen is given by 100 nm or more; a diffusion light which is obtained by a light diffusion body is used as an object light; a non-diffusion light is used as a reference light; and the object light and the reference light are irradiated on a photosensitive material having the thickness of 1 to 20 μm in order to form an interference fringe so that a hologram element is produced.
In still another preferred embodiment, a peak wavelength of the hologram screen is either 525 nm or less, or 585 nm or more; a half bandwidth of a spectral characteristic of the hologram screen is 100 nm or more; a diffusion light which is obtained by a light diffusion body is used as an object light; a non-diffusion light is used as a reference light; the object light and the reference light are irradiated on a photosensitive material in order to form an interference fringe; and a refractive index of the photosensitive material is adjusted so that a hologram element is produced.
In still another preferred embodiment, the diffusion light which is obtained by the light diffusion body is used as the object light; the non-diffusion light is used as the reference light; the object light and the reference light are irradiated on the photosensitive material in order to form the interference fringe; and a heat treatment is performed for the photosensitive material in the extent of 80°C to 150°C C. so that a hologram element is produced.
In still another preferred embodiment, the diffusion light which is obtained by the light diffusion body is used as the object light; the non-diffusion light is used as the reference light; a sum of an exposure intensity of the object light and the exposure intensity of the reference light is defined in the extent of 0.02 to 50 mW/cm2; the object light and the reference light are irradiated on the photosensitive material in order to form the interference fringe so that a hologram element is produced.
In still another preferred embodiment, the diffusion light which is obtained by the light diffusion body is used as the object light; the non-diffusion light is used as the reference light; an intensity ratio (R/O) of the intensity (O) of the object light and the intensity (R) of the reference right is defined by 0.1 to 30; and the object light and the reference light are irradiated on the photosensitive material in order to form the interference fringe so that a hologram element is produced.
In still another preferred embodiment, a peak wavelength of the hologram screen is either 525 nm or less, or 585 nm or more; a diffusion light which is obtained by a light diffusion body is used as an object light; a non-diffusion light is used as a reference light; the object light and the reference light are irradiated on a photosensitive material in order to form an interference fringe; and a thickness of of the photosensitive material is adjusted so that a hologram element is produced.
In still another preferred embodiment, a peak wavelength of the hologram screen is either 525 nm or less, or 585 nm or more; a diffusion light which is obtained by a light diffusion body is used as an object light; a non-diffusion light is used as a reference light; an incident angle θr of the reference light to a photosensitive material is different from an incident angle θe of the image light to the hologram screen; and the object light and the reference light each having the above different angle are irradiated on the photosensitive material in order to form an interference fringe so that a hologram element is produced.
In still another preferred embodiment, an amount of angle correction which indicates a difference between the incident angle θr and the incident angle θe is defined by the extent of -5°C to +5°C.
In still another preferred embodiment, a half bandwidth of a spectrum characteristic of the hologram screen is given by 100 nm or more; a diffusion light which is obtained by a light diffusion body is used as an object light; a non-diffusion light is used as a reference light; and a plurality of object lights each having different angle are irradiated on a photosensitive material in order to form an interference fringe so that a hologram element is produced.
In accordance with a third aspect of the present invention, there is provided a hologram screen for reproducing an image based on an output light obtained by scattering and diffusing an image light from an image projector, characterized in that, a haze ratio is given by 5 to 60%.
In a preferred embodiment, a screen gain of the hologram screen is given by 0.3 or more.
In another preferred embodiment, an intensity ratio ER/EO of the intensity EO of the object light and the intensity ER of the reference light is changed in accordance with a scattering angle of the light diffusion body.
In still another preferred embodiment, when the scattering angle of the light diffusion body is set to a large angle, the intensity ratio ER/EO is set to a small value.
Before explaining preferred embodiments of the present invention, the conventional arts and their problems will be explained in detail with reference to the attached drawings.
On the other hand, it is possible to constitute the hologram screen 11 by using a transparent material. In the case of the transparent hologram screen, the observer can observe not only the image reproduced on the hologram screen 11, but also an object 119 located at the back of the hologram screen 11. As mentioned above, the hologram screen 11 can be widely utilized as a display apparatus having very good visual effect.
The hologram screen 11 can be produced by using an exposure optical system 12 shown in
The object light 1217 and the reference light 1218 are irradiated on a photosensitive material 1220 so that an interference fringe formed by these lights 1217 and 1218 is recorded on the photosensitive material 1220. As a result, the light diffusing body 1216 is recorded on the photosensitive material 1220. When the image light 1120 (see
In the exposure optical system 2 in
However, when the image is reproduced by the conventional hologram screen, for example, although approximately the same color tone as the image light can be obtained at the center of the hologram screen, the color tone becomes more blue than the image light at the upper portion of the hologram screen, and becomes more yellow than the image light at the lower portion of the hologram screen (see COMPARING SAMPLE C1 in the third embodiment). That is, in the conventional art, it is impossible to reproduce uniformly the color of the image light on all areas of the hologram screen. That is, there is a problem in which an unnatural image which gives large feeling of difference to the observer is reproduced in the conventional art.
Accordingly, the first invention aims to provide a hologram screen which can eliminate unevenness of color on the reproduced image, and a producing method of the hologram screen as explained in detail below.
According to the invention, in the hologram screen for reproducing the image based on the output light by scattering and diffusing the image light which is irradiated from the image projector, when a white light is projected on the hologram screen as the image light, and when a value on the CIE 1976 chromaticity coordinate (u', v') is (u'A, v'A) and (u'B, v'B) at optional two points A and B having the distance of 20 cm or less between two points on the hologram screen,
the hologram screen is characterized in that the output light which is output perpendicularly from the surface of the hologram screen has color distribution in which the color difference Δu'v' between two points A and B and delivered from the following formula (1) becomes 0.06 or less.
where, the formula (1) is expressed by,
As mentioned above, A and B are optional two points on the surface of the hologram (i.e., the side in which the output light is output), and the distance between two points is 20 cm or less (see FIG. 2). The color difference at two points can be obtained from the chromaticity coordinate at two points. When the color difference is larger than 0.6, unevenness of color may occur on the reproduced image. Further, it is preferable that the color difference is nearly zero. That is, when the color difference is brought near to zero, it is possible to almost eliminate unevenness of color of the image. In this case, the CIE 1976 chromaticity coordinate (u', v') indicates a value on an orthogonal coordinate of u' and v' which is obtained from the UCS chromaticity coordinate defined by the CIE.
The operation of the first aspect of the present invention will be explained below.
The important point in the first aspect of the present invention lies in that the output light has the color distribution in which the color difference Δu'v' between optional two points A and B having the distance of 20 cm or less becomes 0.06 or less. The maximum color difference of the output light is 0.06 in the present invention, and the difference of the color between the output lights irradiated from each portion is small. Accordingly, the output light from any position on the hologram screen has an approximately uniform color tone so that it is possible to obtain the output light in which the color of the image light is considered. As a result, it is possible to prevent unevenness of color on the hologram screen, such as a blue portion at the upper on the screen and a yellow portion at the lower on the screen, when reproducing the image.
The hologram screen of the first aspect of the present invention can reproduce the color of the image light irradiated on the screen, and it is possible to reproduce the image having no feeling of difference for the observer. Accordingly, the hologram screen according to the first aspect of the present invention can be widely utilized as the screen of various image display apparatus. Further, since it is easy to constitute the hologram screen by using the transparent material, the present invention can be utilized as a display apparatus for displaying both image on the hologram screen and image transmitted from the back. Further, when the image is not displayed on the hologram screen, it is possible to utilize a screen in which the view field is not cut off (i.e., the view field can see through the hologram screen because of the transparent material).
The hologram screen according to the first invention can be utilized as a screen for advertisement provided for various show windows or a screen for navigation system provided in a vehicle, etc. Further, as the image projecting apparatus 112, it is possible to utilize various projectors and liquid crystal projectors. Still further, as the image light, it is possible to utilize various advertisements and environmental images without kinds of images. Still further, regarding the color difference, it is preferable to satisfy the color difference not only in the case of the front of the hologram screen (see FIG. 3), but also in the cases of upper, lower, left and right directions of the hologram screen.
According to the invention, the hologram screen is characterized in that the output light output from the surface of the hologram screen to a viewpoint provided based on the following formula (2) has color distribution in which the color difference Δu'v' between two points A and B and delivered from the above formula (1) becomes 0.1 or less.
where, the formula (2) is expressed by,
In this case, L is the distance between the viewpoint and the center of the hologram screen, and H is a height of the hologram screen itself.
When the color difference is larger than 0.1, unevenness of color may occur on the reproduced image. Further, it is preferable that the color difference is nearly zero. That is, when the color difference is brought near to zero, it is possible to almost eliminate unevenness of color of the image. The maximum color difference of the output light toward the viewpoint determined based on the formula (2) is 0.1, and the difference of the color between each output lights is small. Accordingly, when the image light has a single color, the output light generated from any portion on the hologram screen has approximately the same color tone each other. As a result, it is possible to obtain the output light in which the color of the image light is reflected. As mentioned above, as a result, it is possible to prevent unevenness of color on the hologram screen, such as a blue portion at the upper on the screen and yellow portion at the lower on the screen, when reproducing the image.
According to the invention, it is preferable that, as the spectral characteristic of the output light which is output perpendicularly from the surface of the hologram screen, either the difference in peak wavelengths at all areas of the hologram screen is 120 nm or less, or the difference in half bandwidth is 100 nm or less.
When the difference in the peak wavelength is larger than 120 nm, the output light from the hologram screen is constituted by the light having more wide range of the wavelength. As a result, the difference of the color on the hologram screen become large so that unevenness of color easily occurs in the reproduced image. Further, it is preferable that the difference in the peak wavelength is nearly zero.
When the half bandwidth is larger than 100 nm, the wavelength distribution of the output light from the hologram screen becomes narrow, and the wavelength distribution from another portion becomes wide. That is, the output light from the hologram screen is constituted by the light having more wide range of the wavelength so that the difference in the color becomes large and unevenness of color easily occurs in the reproduced image. Further, it is preferable that the difference in the half bandwidth is nearly zero.
In the above explanation, the description "the difference in peak wavelengths at all areas of the hologram screen is 120 nm or less" means that, when collecting the spectral characteristics of the output light from the hologram screen, the difference in the peak wavelength between one spectral characteristic having longest peak wavelength and another spectral characteristic having shortest peak wavelength is 120 nm.
Regarding the half bandwidth, the description "the difference in half bandwidth is 100 nm or less" means that the difference in half bandwidth between one spectral characteristic having the most wide half band and another spectral characteristic having the most narrow half band is 100 nm.
According to the invention, in the exposure optical system using the object light and the reference light, the object light being the diffusion light obtained by using the light diffusion body and the reference light being a non-diffusion light, the hologram screen is produced by irradiating the object light and the reference light onto the photosensitive material in order to expose the photosensitive material.
At that time, a method of producing the hologram screen according to the present invention is characterized in that the photosensitive material having a thickness distribution which is inclined to the incident direction of the reference light (see 1220 in FIG. 11). This means that the thickness of the photosensitive material is different between the upper portion and the lower portion. In this case, the incident direction of the reference light is indicated by the directions (1), (2) and (3) in FIG. 11.
In this case, there is a known fact that the half bandwidth becomes wider in the spectral characteristic of the hologram screen made by the thin photosensitive material, and the spectral characteristic becomes broader. This is obvious from the following logical formula for defining the half bandwidth.
where, Δλ is a half bandwidth, λ0 is a recorded wavelength, T is a thickness of the photosensitive material, n is a refractive index of the photosensitive material, and θr is an incident angle of the reference light.
The spectral characteristic of the hologram screen made by the photosensitive material having the uniform thickness in a conventional art is shown in FIG. 14. In this spectral characteristic, the half bandwidth becomes broader in order of (1)→(2)→(3). For example, when putting all spectral characteristics into the spectral characteristic (2), the photosensitive material for the spectral characteristic (1) having a narrow half bandwidth is thinned, and the photosensitive material for the spectral characteristic (3) having a broad half bandwidth is thickened.
As mentioned above, it is possible to obtain the hologram screen having the uniform spectral characteristic by providing the photosensitive material having the different thickness between the upper portion and the lower portion.
In this case, the difference in the color of the output light from each portion of the hologram becomes small so that it is possible to obtain the output light having almost the same color tone.
As is obvious from the above, according to the invention, it is possible to provide a producing method of the hologram screen having no unevenness of color in the reproduced image. Further, the present invention has the same effect as the above, for not only the incident direction of the reference light, but also an orthogonal direction, i.e., the right and left directions when reproducing the image on the hologram screen.
As the photosensitive material, it is possible to utilize various materials, for example, various kinds of photopolymers, a dichromated gelatin, a silver salt, etc. Further, as the light diffusion body, it is possible to utilize any kinds of materials, for example, a ground glass, an opal glass, etc.
Next, according to the invention, as the photosensitive material, it is preferable to use the material in which the larger the incident angle of the reference light, the larger the thickness distribution.
As shown in
When the half bandwidth of the spectrum characteristic of the output light from the hologram screen is widened, the wavelength distribution of the output light can be broadened so that it is possible to increase reappearance of the color of the image light. Further, it is possible to avoid reduction of the reappearance of the color of the image light caused by the difference of the peak wavelength in the spectrum characteristic.
As mentioned above, when the thickness of the photosensitive material becomes thin, the spectral characteristic of the output light becomes broad. That is, selectivity of the wavelength for the incident light becomes small so that it is possible to diffract the broader wavelength (i.e., the half bandwidth becomes broad.). However, since the number of the interference fringe which can record is reduced in the case of the thin photosensitive material, the hologram screen having low effectivity is obtained.
On the other hand, when the thickness of the photosensitive material becomes thick, the selectivity of the wavelength becomes large (i.e., the half bandwidth becomes narrow.). However, since the number of the interference fringe which can record is increased in the photosensitive material, the hologram screen having high effectivity can be obtained. Accordingly, by providing the thickness distribution having different thickness at the upper portion and the lower portion, it is possible to arrange all spectrum distributions of the hologram screen, and to match the whole efficiency of the hologram screen. In this case, the difference of the color of the output light from each portion of the hologram screen becomes small so that it is possible to obtain the output light having almost the same color tone.
According to the invention defined claim 6, it is preferable that the thickness distribution of the photosensitive material is given by ΔT≦0.5T0, where, ΔT is a difference in thickness between the upper end and the lower end in the photosensitive material. According to this conditions, it is possible to ensure the effect of the present invention. If the ΔT is larger than 0.5T0, the range of the thickness distribution of the hologram screen becomes too wide so that it may be very difficult to obtain the effect of reduction of unevenness of color.
It is preferable that an inclined degree k of the thickness of the photosensitive material is given by 0<k≦2×10-5. Where, the inclined degree k is given by a value when a primary approximation is executed to the thickness distribution of the photosensitive material. When the inclined degree "k" of the thickness becomes larger than 10-5, an amount of shift of the peak wavelength in the spectrum distribution of the output light becomes too large so that the difference occurs in the color of the output light and the improved effect of unevenness of color may be reduced.
According to the invention, it is preferable to establish the following formula (4) in the thickness distribution, i.e.,
where, T is the thickness at optional location of the photosensitive material, T0 is the thickness at a center of the photosensitive material, R is an incident distance of the reference light at optional location of the photosensitive material, R0 is the incident distance of the reference light at the center of the photosensitive material, θ0 is the incident angle of the reference light at the center of the photosensitive material, and "b" is a coefficient determined by the thickness distribution and defined as 0<b<1.
The photosensitive material having the thickness distribution satisfying the above conditions becomes linearly thin from the thick portion until the thin portion. By using the above photosensitive material, the brightness and color on the image are not changed partially, and it is possible to obtain the hologram screen in which, for example, stripe-like unevenness of color does not occur on the screen.
In the thickness distribution, even if there is unevenness in the range of 15% of the thickness T0 at the center of the photosensitive material, there is no problem of the stripe-like unevenness of color.
According to the invention, in the exposure optical system using the object light and the reference light, the object light being the diffusion light obtained by using the light diffusion body and the reference light being the non-diffusion light, the hologram screen is produced by irradiating the object light and the reference light onto the photosensitive material in order to expose the photosensitive material.
At that time, a method of preparing the hologram screen according to the present invention is characterized in that the photosensitive material which is previously irradiated by an ultraviolet in accordance with energy distribution inclined to the incident direction of the reference light is used as the hologram screen.
Further, there is a material which can stop polymerization action of monomer by irradiating the ultraviolet in the photosensitive material. For this material, it is possible to reduce the sensitivity by previously irradiating the ultraviolet having the intensity in which the polymerization action of the monomer is not completely stopped.
According to the invention, it is preferable to satisfy the following formula (5) as the energy distribution of the ultraviolet regarding the incident distance R of the reference light at the optional location on the photosensitive material.
where, Euv is an amount of energy of the ultraviolet irradiated to the optional location on the photosensitive material, R0 is an incident distance of the reference light at the center of the photosensitive material, and E0 is an amount of energy of the ultraviolet irradiated to the center of the photosensitive material. As a result, it is possible to obtain the photosensitive material having the optimum sensitivity.
According to the invention, in the exposure optical system using the object light and the reference light, the object light being the diffusion light obtained by using the light diffusion body and the reference light being the non-diffusion light, the hologram screen is produced by irradiating the object light and the reference light onto the photosensitive material in order to expose the photosensitive material.
At that time, a method of producing the hologram screen according to the present invention is characterized in that the incident distance of the reference light at the optional location of the photosensitive material is shorter than the incident distance of the image light input from the image projector when reproducing the image on the hologram screen.
The incident angle θ0 and the incident distance R0 at the center of the photosensitive material when producing the hologram screen is usually set to the same value as an incident angle f0 and an incident distance F0 at the center of the hologram screen when irradiating the image light on the hologram screen and reproducing the image (see FIGS. 1 and 10).
In the producing method according to the present invention, the incident distance R0 of the reference light is set to the distance shorter than the incident distance F0 so that it is possible to set the incident angle of the reference light, except for the center of the photosensitive material, to a value different from the incident angle of the image light.
That is, the incident angle of the image light coincides with the incident angle of the reference light at the center of the photosensitive material, but, except for the center, the incident angle of the image is different from the incident angle of the reference light. At that time, the difference in distance of the above is changed in accordance with the distance from the center of the photosensitive material.
As shown in
When the incident angle of the reference light is different from the incident angle of the image light, there is known wavelength shift which is expressed by the following logical formula (6) in the spectrum characteristics of the hologram screen.
As shown in
From the above formula (6), the following formula can be obtained.
As is obvious from the above formula, when the incident angle θR1 of the reference light is smaller than the incident angle θy of the image light, the output light is shifted to a side of the long wavelength. On the other hand, when the incident angle θR1 is larger than the incident angle θy, the output light is shifted to the side of the short wavelength.
As the hologram screen in which the incident angle of the reference light is equal to the incident angle of the image light, there is a comparing sample C1 explained in the third embodiment. The spectral characteristic of this sample is shown in FIG. 14. If the spectral characteristic of this hologram screen is arranged to the spectral characteristic of the curve (2), the spectral characteristic of the curve (1) is shifted to the side of the long wavelength and the spectral characteristic of the curve (3) is shifted to the side of the short wavelength.
That is, the incident angle of the reference angle is set to the angle smaller than the incident angle of the image light in the spectral characteristic (1), and the incident angle of the reference angle is set to the angle larger than the incident angle of the image light in the spectral characteristic (3). This can be realized by shortening the incident distance of the reference light than the incident distance of the image light. In this case, the incident angle of the reference light is maintained to the same value of the incident angle of the image light at the center of the photosensitive material.
As a result, since the spectral characteristic of the hologram screen can be arranged in the whole, the difference of color of the output light from each portion of the hologram screen becomes small, and it is possible to obtain the output light having approximately the same color tone.
According to the invention, in the exposure optical system using the object light and the reference light, the object light being the diffusion light obtained by using the light diffusion body and the reference light being the non-diffusion light, the hologram screen is produced by irradiating the object light and the reference light onto the photosensitive material in order to expose the photosensitive material.
At that time, a method of producing the hologram screen according to the present invention is characterized in that an intensity ratio IR/IO of the reference light and the object light has the following relationship is given by the following formula, i.e., IR/IO≦10, where, IR is the intensity of the reference light, and IO is the intensity of the object light.
In this embodiment, the ratio IR/IO is 10 or less. When the intensity ratio IR/IO becomes large, the intensity of the object light becomes very weak. As a result, the dispersion of the spectral characteristic, which is caused by the dispersion of the intensity of the object light due to the location on the photosensitive material, is easy to occur on the hologram screen. That is, the difference of the spectral characteristic due to the intensity of the object light becomes large.
When the intensity of the object light becomes large, the spectral characteristic becomes approximately constant so that the smaller the ratio IR/IO, the smaller the difference of the spectral characteristic. As a result, it is possible to arrange the spectral characteristic in the whole of the hologram screen. Further, the difference of color of the output light from each portion of the hologram screen becomes small so that it is possible to obtain the output light having approximately the same color tone.
According to the invention, in the exposure optical system using the object light and the reference light, the object light being the diffusion light obtained by using the light diffusion body and the reference light being the non-diffusion light, the hologram screen is produced by irradiating the object light and the reference light onto the photosensitive material in order to expose the photosensitive material.
At that time, a method of producing the hologram screen according to the present invention is characterized by at least two sets of the following features (A) to (D), i.e.,
(A): to use the photosensitive material having the thickness distribution inclined to the incident direction of the reference light,
(B): to use the photosensitive material which is previously irradiated by the ultraviolet in accordance with the energy distribution inclined to the incident direction of the reference light,
(C): to determine the incident distance of the reference light at the optional location on the photosensitive material so as to become shorter than the incident distance of the image light input from the image projector when reproducing the image on the hologram screen, and
(D): to have the relationship of the ratio IR/IO≦10 in the intensity of the reference light and the object light in the whole of the surface of the photosensitive material.
According to the features (A) to (D), it is possible to obtain the hologram screen having the arranged spectral characteristic. As mentioned above, by performing at least two sets of features (A) to (D), it is possible to make the difference of color eye small, and to satisfy the desired hologram characteristic, although it is very difficult to realize small difference of color in the case of any one feature from (A) to (D) depending on the desired hologram characteristic (for example, a view angle, a brightness of an image to be reproduced, etc.).
The first embodiment will be explained in detail with reference to
As shown in
the output light 1121 output perpendicularly from the surface of the hologram screen has color distribution in which the color difference Δu'v' between two points A and B and delivered from the above formula (1) becomes 0.06 or less.
Next, one example in use of the hologram screen will be explained below. As shown in
Further, it is possible to prepare the hologram screen 11 by using the transparent material. In this case, the observer 18 can observe not only the image reproduced by the hologram screen 11, but also the object 119 at the back of the hologram screen 11. The hologram screen 11 in
The hologram screen according to the first embodiment was tested in accordance with the following processes.
First, the hologram screen 11 having a size of 300 nm×400 nm was prepared. In this case, as shown in
The color difference Δu'v' was measured in accordance with the following steps.
As shown in
Further, as shown in
Next, how to obtain the color difference Δu'v' using the spectral characteristic is explained below. In this case, the CIE 1976 chromaticity coordinate (u', v') is used in the following steps.
The chromaticity coordinate u' is expressed below, i.e.,
In the above formula, for example, X can be obtained from the formula shown in
As a result of the above measurement, next test was performed using the hologram screen having the maximum color difference of 0.01 to 0.08. In this case, although the color difference can be obtained from the spectral characteristic, it is possible to obtain the color difference by directly measuring the chromaticity using a colorimeter.
As shown in
A result of observation is shown in FIG. 6. The image was evaluated by twenty observers in accordance with a subjective evaluation grade having seven grades 1 to 7 (see 1 to 7 in FIG. 6). In this case, ten minutes is required for getting good condition for eye and correctly recognizing presence or absence of unevenness of color. The measurement was performed within a room, and no lamp was provided in the room. The brightness of the white color to be projected was 300 cd/m2. A frosted black wall 119 was provided at the back of the hologram screen 11.
As shown in
In this test, no lamp is provided and the background light is the black which is very close to zero. When the illuminance within the room is 500 Lux (this is an average illuminance in offices), and when the white wall paper is used at the back of the hologram, the level 4 in this test becomes the same level as the level 5 or more, i.e., the observer does not mind unevenness of color. Further, when the color difference is 0.07 or more, there is the observer who does mind unevenness of color in this test. As is obvious from the above, when the color difference is 0.06 or less, it is obvious that the observer does not mind unevenness of color of the image on the hologram screen.
Next, the effect of the first embodiment will be explained below. As mentioned above, the output light has color distribution in which the color difference Δu'v' between points A and B is 0.06 or less. That is, since the difference of color is small, the output light from any location on the hologram screen has the same color tone each other, if the incident light is the monochrome. That is, there is no phenomenon from which color at a part of the hologram screen are different. As a result, as shown in
The spectral characteristic was checked for the hologram screen having the color difference 0.06. In this case, when the half bandwidth is the same, the difference of the peak wavelength corresponds to approximately 120 nm. On the other hand, when the peak wavelength is the same, the difference of the half bandwidth corresponds to approximately 100 nm. As is obvious from the above when the color difference on the hologram screen is not measured, the conditions for the color difference can be satisfied if the spectral characteristic is smaller than the above difference.
As shown in
In the hologram screen according to the second embodiment, the output light, which is emitted toward the viewpoint, has the color distribution in which the color difference between two points is 0.1 or less. As well as the first embodiment, shown in
As shown in
The measurement of the color difference will be explained in detail below. As shown in
The white light 1130 is diffracted on the hologram screen 11 so that the output light 1131 can be obtained. In this case, the spectral characteristic of the output light 1131 at the location apart by the distance L from the center 1109 of the hologram screen 11 was measured. In order to measure the spectral characteristic of the output light 1131, first, the output light from the point 1108 is measured by providing the light receiving device 1179 on the line between the viewpoint 180 and the point 1108. That is, the light receiving device 1179 is inclined by the same angle as that of the line between the viewpoint 180 and the point 1108. As a result, the spectral characteristic is measured, and the color difference can be obtained by the same method as the first embodiment. In this case, the output light from the center 1109 is output perpendicularly from the surface of the hologram screen 11, as well as the first embodiment.
The color difference was re-checked based on the above method regarding the hologram screen having the color difference 0.06 in the first embodiment. As a result, when H=300 mm, and L=2000 mm, in the structure of the hologram screen, the color difference was changed from 0.06 to 0.1 in the second embodiment. Further, since the hologram screen having the color difference 0.06 in the first embodiment was evaluated as the level 5 or more (i.e., the observer does not mind unevenness of color), it is obvious that there is no unevenness of color on the reproduced image for the hologram screen having the color difference 0.1. Since these measuring methods can be used to measure the color difference which can be observed actually through a human eye, it is possible to perform practical evaluation.
As shown in
As shown
First, the exposure optical system in
As shown in
In this case, in the exposure optical system 2 shown in
The hologram screen 11 was made by exposing two kinds to photosensitive materials using the exposure optical system 12. The photosensitive material of the sample 1 has the thickness distribution shown in FIG. 12. That is, the sample 1 has the inclined thickness, i.e., the thickness is different between one end and the other end of the photosensitive material. In
The sample 1 and the comparing sample C1 were provided to the exposure optical system 2 shown in
The measurement of the spectral characteristic of the hologram screen having the sample 1 and the comparing sample C1 is explained with reference to
When the hologram screen was observed based on the same conditions as the first embodiment, unevenness of color was not almost recognized in this embodiment. As mentioned above, by using the photosensitive material having the inclined thickness distribution, it is possible to obtain the hologram screen having no unevenness of color when reproducing the image. Further, as shown in
The maximum color difference was measured by using the same method as the first embodiment. As a result of measurement, the maximum color difference became 0.073. Further, the unevenness of color was tested for this hologram screen. As a result, all observers answered level 3 or more (i.e., the observer slightly do mind the unevenness of color.). As is obvious from the above, the difference in the spectral characteristic at each portion of the hologram screen is caused of unevenness of color when reproducing the image on the hologram screen.
As shown in
The above irradiation method of the ultraviolet will be explained in detail with reference to
As a result, an amount of absorption of the photosensitive material at the wavelength 414 nm was changed in accordance with the distance P as shown in FIG. 17. In
In the above conditions, the color difference between optional two points (see the first embodiment) on the hologram screen was 0.023 in maximum. Further, unevenness of color cannot be recognized when observing the hologram screen in accordance with the same conditions as the first embodiment. Further, the peak wavelength in the spectral characteristic of the hologram screen was measured at the points (1), (2) and (3) in FIG. 3. Further, when the ultraviolet is not irradiated, the spectral characteristic was also measured in order to compare irradiation with non-irradiation of the ultraviolet. As a result, in the case of the spectral characteristic (1), the wavelength 460 nm (in the case of non-irradiation) was 462 nm (in the case of irradiation). In the case of the spectral characteristic (2), the wavelength 510 nm (in the case of non-irradiation) was 480 nm (in the case of irradiation). In the case of the spectral characteristic (3), the wavelength 510 nm (in the case of non-irradiation) was 488 nm (in the case of irradiation).
The relationship between an amount of irradiation of the ultraviolet and reduction of sensitivity is explained using the photopolymer made by Dupont Co., Ltd., below.
As shown in
Accordingly, by preferably setting the amount of the energy of the ultraviolet to be irradiated, it is possible to arrange the spectral characteristic of the hologram screen, and to reduce unevenness of color until the grade which is difficult to recognize the same. Further, if the spectral characteristic is intended to bring it near to that of (2), it is possible to shift the whole to the long wavelength side by changing the incident angle of the reference light at the exposure and the incident angle of the reproducing light at the reproduction, and by setting the incident angle of the reference light so as to become small. In this case, it is possible to realize a predetermined effect in the difference of the angle of 1 to 2°C.
As shown in
The performance of the hologram screen which was made by shortening the distance of the reference light was evaluated as follows. First, the exposure optical apparatus was prepared as shown in FIG. 10. In this case, the incident angle θ0 of the reference light 1218 was set to 40°C, and the incident distance R0 of the reference light was set to 1700 mm. Then, the photosensitive material was exposed. Further, the photosensitive material 1220 in which the exposure was completed, was replaced to new one. Further, the exposure was performed after the incident distance R0 of the reference light was shortened to the distance R0' as shown in FIG. 20. In this case, a photopolymer made by Dupont Co., Ltd. was used as the photosensitive material 1220 having the uniform thickness distribution and the size of 300 mm×400 mm as shown by the comparing sample C1 in
Based on the above conditions, each peak wavelength at the spectral characteristic of each hologram screen, in which the incident distance R0 of the reference light was shortened, was measured as shown in FIG. 23. In
Further,
In this embodiment, as shown in
In this structure, when the divergence light from the object lens 1221 is input to the convex lens 141, this light becomes the convergence light so that this light is focused on the light path. As an effect of the convex lens, it is possible to shorten the incident distance of the reference light, for example, the distance -700 mm, without change of the physical location of the photosensitive material 1220 and the object lens 1221. In this embodiment, other conditions are the same as the fifth embodiment.
When the convex lens 141 is provided as mentioned above, it is not necessary to limit the divergence point of the reference light 1218 to the location of the distance 1700 mm from the center 1229 of the photosensitive material 1220, and to freely change the location of the object lens 1221 and the photosensitive material 1220 in accordance with the f-value of the lens to be used. In
The cylindrical lens is very effective in the case that the color difference is reduced for the incident direction of the reference light, but the color difference is not reduced for the direction perpendicular to the surface of the drawing sheet (FIG. 26). This is because, when the distance of the reference light is shortened in order to arrange the peak wavelength at the points (1), (2) and (3) in
In this embodiment, in all areas on the photosensitive material, the intensity ratio of the reference light and the object light is defined as IR/IO<10 (where, IR is the intensity of the reference light, and IO (is the intensity of the object light). That is, as shown in
As other conditions, the incident angle of the reference light to the center 1229 of the photosensitive material 1220 was set to 40°C, and the incident distance of the reference light was set to 1350 mm. Further, the photopolymer made by Dupont Co., Ltd. having the uniform thickness distribution and the size of 300 mm×400 mm, as shown in
The relationship of the maximum value of the color difference and the intensity ratio IR/IO between optional two points on the hologram screen is shown in FIG. 29. As shown in
The second aspect of the present invention relates to a method for producing a hologram element which can be used as a display apparatus for displaying a still image or an animated image by irradiating the image light.
The object light 214 and the reference light 216 are irradiated on the photosensitive material 230 and exposed by using an exposure optical system 29 as shown in
On the other hand, in general, a large size screen has been desired as the display apparatus in order to utilize as an advertizing board in a showroom. However, it is very difficult to produce a large size hologram screen by using the exposure optical apparatus 29 as mentioned above in once projection of the image. That is, although it is necessary to provide a large size photosensitive material in order to produce the large size hologram screen, a lot of time is required for exposure of the photosensitive material. Further, since it is necessary to irradiate the reference light onto the whole of the large size photosensitive material, the intensity of the reference light becomes weak so that the exposure time also becomes long. As a result, the exposure time may exceed the time for stably maintaining the interference fringe on the photosensitive material so that the production efficiency of the hologram element deteriorates.
Further, it is necessary to utilize the large size light diffusion body in order to obtain the object light which can be irradiated on the whole of the large photosensitive material. However, it is very difficult to produce the large light diffusion body. Still further, since the object light which is obtained by the large size photosensitive material is formed by the diffusion light which is diffused in the wide extent, the light intensity becomes weak so that the exposure time for exposing the photosensitive material becomes long.
In order to resolve the above-mentioned problems, the inventor has proposed two methods, i.e., (1) a method of resolving problems by reducing a size of the photosensitive material, and (2) a method of resolving problems by reducing a size of the light diffusion body, in Japanese Unexamined Patent Publication No. 9-349572.
In the method (1), as shown in
In the method (2), as shown in
There is a problem, however, in the method (2). That is, when combining the method (1) with the method (1), it is impossible to perform sufficient recording on the photosensitive material from the light diffusion body imaged on the mirror, and there is the difference in brightness between an area directly recorded by the light diffusion body and another area indirectly recorded by the light diffusion body through the mirror. As a result, depending on the angle observed by the observer, the image on the hologram screen becomes partially dark, and color are changed. Further, a boundary line between the diffusion body and the mirror may be imaged on the hologram screen so that the observer may has uncomfortable feeling when observing image on the hologram screen.
According to the producing method of the second invention, it is possible to display uniform and bright image on the display apparatus, and to observe the image in the broad angle without changes of brightness and color eye.
According to the invention, the hologram element is formed by interferencing the reference light with the object light transmitted through the light diffusion body, and by recording the light diffusion body on the photosensitive material in the optical system. There is a mirror arranged approximately perpendicularly to the light diffusion body on the light diffusion body. Further, a rotational center is defined by an axis intersected perpendicularly to the center of the photosensitive material, and the photosensitive material and the light diffusion body are arranged with the angle θ.
According to the second aspect of the present invention, polarized direction of laser light is determined by either P-polarization or S-polarization which are inclined from θ-5 to θ+5. That is, as the feature of the present invention, either P-polarization or S-polarization having the polarized direction in the range of the angle θ-5 to θ+5 is used as the laser light.
When the polarized direction is out of the this range, the light diffusion body which is imaged on the mirror becomes dark, the image becomes partially dark depending on the observer's angle.
The operation of the second aspect of the present invention will be explained below. The mirror is arranged perpendicular to the light diffusion body used in the present invention (see FIGS. 31 and 32). In the recording of the light diffusion body on the photosensitive material, the object light is irradiated from the light diffusion body, a part of the object light is irradiated directly on the photosensitive material, but other object light is irradiated on the photosensitive material after reflected by the mirror. Accordingly, the incident angle of the object light on the photosensitive material becomes broad by using the above compact light diffusion body so that it is possible to obtain the object light having broad extent as well as the large size light diffusion body.
Further, when producing the hologram element, the light diffusion body and the photosensitive material are rotated with the same angle θ around the axis which is intersected perpendicularly to the center point of the photosensitive material and used as the center of the rotation.
In this case, when the large size hologram screen 3 shown in
In
In
Accordingly, when producing the hologram element, the light diffusion body and the photosensitive material are rotated with the same angle θ as mentioned above. Further, the reference light is irradiated to the photosensitive material on the same horizontal plane as the object light. When θ=θb, it is possible to easily and safety produce the hologram element since the optical system for exposing the photosensitive material can be easily provided.
In the present invention, either the P-polarization or the S-polarization having the polarization direction in the extent from the angle θ-5 to θ+5 is used as the laser light, as shown in FIG. 33. In this case,
There are the light diffusion body 220 and the mirrors 221 to 224 provided thereto, which are rotated with the angle θ around the axis intersected perpendicularly to the center point of the light diffusion body 220 and used as the rotational center as shown in FIG. 41. In this case, since the polarized direction of the laser light is not changed and directed by the arrow line LO, the perpendicular direction (i.e., S-polarization) is maintained.
The laser light is transmitted through the light diffusion body 220 as shown in
In this case, the polarized direction of the reference light which reaches the photosensitive material is the same as that of the laser light and has the S-polarization. Accordingly, in the object light Ob after reflection, the object light which can contribute to form the interference fringe with the reference light, as shown in
As mentioned above, the sufficient recording to the photosensitive material cannot be performed from the light diffusion body which was imaged on the mirror, and the difference in brightness occurs between the recorded area directly imaged by the light diffusion body and the recorded area indirectly imaged by the light diffusion body through the mirror. As a result, there is a problem in which the image becomes partially dark on the hologram screen, depending on the observing angle from the observer.
In the present invention, as mentioned above, the P-polarization or the S-polarization having the polarized direction in the range from the angles θ-5 to θ+5 is used as the laser light. Accordingly, it is possible to provide the state of the P-polarization or S-polarization for the light diffusion body and the mirror inclined with the angle θ. That is, in the present invention, the object light is reflected by the mirror so that the large change of the polarization direction is prevented, and it is possible to prevent a partially dark image which depends on the observing angle from the observer.
In the S-polarization, for example, in
The laser light used in the present invention is generated by a known laser oscillator, and it is possible to prepare the P-polarization or the S-polarization having the polarized direction in the range from the angles θ-5 to θ+5 by providing a half-wave plate for the laser oscillator. The wavelength plate is an optical element which can change the polarization state of the optical wave by providing the phase difference based on the difference in the refractive index for the polarized component of the optical crystal having the optical anisotropy. Further, the half-wave plate is an optical element which can change the polarized direction of the linear polarization.
When the linear polarized light is irradiated with the angle θ for the optical axis of the half-wave plate, the polarized direction of the output light has the direction which is inclined with the angle 2×θ for the incident light. Further, the angle θ can be changed continuously. As a result, it is possible to easily obtain the laser light having the desired polarized direction. Further, it is possible to utilize the wavelength plate having the above function utilizing the optical anisotropy of the optical crystal as the half-wave plate. Further, it is possible to utilize a Fresnel rhomb plate which utilizes the total reflection in the optical element as the half-wave plate. Particularly, the Fresnel rhomb wavelength plate can be used for the high power laser light, and can be used widely since the usable wavelength band of the laser light is wide. Accordingly, the Fresnel rhomb wavelength plate can be preferably used as the half-wave plate.
Further, as a method for integrating a plurality of hologram elements, for example, there are two representative methods, i.e., one being a method for bonding the hologram element to a predetermined film (for example, a PTE film) with an adhesive material, and the other being a method for bonding the hologram element to a large glass plate using a transparent and optical adhesive material. Further, it is possible to utilize the light which is generated by an argon (Ar) laser oscillator as the laser light. Further, it is possible to utilize the photopolymer, or the dichromated gelatin, etc., as the photosensitive material. Still further, it is possible to utilize ground glass or opal glass as the light diffusion body.
According to the second invention, it is possible to produce the transparent hologram element in order to form the hologram screen. In this case, it is possible to obtain the transparent hologram screen by using a transparent adhesive material. As a result, the display apparatus having the hologram screen can be effectively used as, for example, not only an advertising board for a show window, showroom, etc., in a shopping center, but also as a transparent screen which can see through an opposite person when the display apparatus is not used, in a ticket window.
Preferable embodiments in the second embodiment will be explained in detail with reference to the attached drawings.
The first embodiment will be explained in detail with reference to
In the optical system shown in
When producing the hologram elements, the mirrors 221 to 224 are provided perpendicularly to the light diffusion body 220 thereon as shown in
In the optical system 21 shown in
After one separated light 212 became the divergence light 2130 by the object lens 2103, and the divergence light 2130 becomes the parallel light 213 by the parabolic mirror 2104. Further, the diffusion light is formed after the parallel light 213 was passed through the light diffusion body 220, and becomes the object light 214. Further, when another separated light 215 is passed through the object lens 2105 so that the reference light 216 can be obtained.
As shown in
As shown in
When the object light 214 and the reference light 216 are irradiated on the photosensitive material 230, the interference fringe formed by these lights is recorded on the photosensitive material 230. As a result, the light diffusion body 220 is recorded on the photosensitive material 230 so that the hologram screen is formed thereon.
Next, the hologram elements 231 to 234 each having width across corners of twenty inches were prepared in accordance with the above-mentioned method as explained below. In this case, the rotational angle θ is different each other in four hologram screens. For example, in
The method for coupling the hologram screens 231 to 234 will be explained in detail below. As shown in
After the above steps, the transparent PET film 242 was bonded to the remaining three hologram screens 232, 233 and 234. Further, as shown in
Next, the display apparatus 235 using the hologram screen 23 according to the second invention will be explained in detail below.
As shown in
Further, the hologram elements 231 to 234 are formed by the transparent material, and the adhesive material for these hologram elements is the transparent PET films 242 and 243. Accordingly, the observer can observe the background 2381 as well as the image on the hologram screen.
The operation of this embodiment will be explained in detail below. As shown in
Accordingly, the incident angle of the object light to the photosensitive material becomes wide so that it is possible to obtain the object light having the same extent as the large light diffusion body by using the small light diffusion body according to this embodiment.
As mentioned above, four hologram elements are produced separately, and integrated to form the hologram screen. When producing the hologram screen, the light diffusion body and the photosensitive material are rotated by the same angle θ. In this case, the angle θ is different in each of four hologram elements. Further, the reference light and the object light are irradiated to the photosensitive material on the same horizontal plane.
Further, in this embodiment, the S-polarization having the polarized direction of the angle θ as the laser light. Accordingly, it is possible to set the polarized direction of the object light to the S-polarization for the light diffusion body and mirrors which are inclined by the angle θ. That is, according to this embodiment, since it is possible to prevent large change of the polarized direction due to the reflection of the object light by the mirror, it is possible to prevent a partially dark portion on the hologram screen and a partially dark image which occurs depending on the observing angle by the observer. As a result, it is possible to display uniform and bright image on the hologram screen and to observe the image from the wide angle without change of the brightness and the color eye.
The second embodiment according to the second aspect of the present invention will be explained with reference to
As shown in
That is, in
In order to investigate in detail, a color brightness meter was arranged at the location of the observer's eye 238 as shown in
In
Before describing the preferred embodiments, a conventional art and its problem are explained below. For example, a known hologram screen formed by the hologram elements has been disclosed in the Japanese Examined Patent Publication No. 52-12568. The above hologram screen is formed by the hologram element and the substrate for reinforcement in which the hologram element is bonded. As shown in
However, in the conventional hologram screen, the reproduced color tone of the image is different from the color tone of the image light 331 which is generated from the image projector 33. For example, the reproduced image becomes slightly green so that the quality of image deteriorates. This is because, as shown in
In the above mentioned document, i.e., JPP-52-12568, the laser oscillator which can generates red, green and blue light is provided in the exposure optical system 310, and one photosensitive material 3120 is multiply exposed by the red, green and blue lights, in order to resolve the above problem. Further, there is another method which has been already disclosed. That is, according to this method, the red, green and blue laser lights are separately used for exposing each photosensitive material, and three photosensitive materials each of which was exposed by the red, green and blue lights, are laminated each other so that one hologram element is produced.
In this method, however, it is necessary to prepare at least three laser oscillators each of which can generate the red, green and blue laser lights, or each of which can generate three kinds of wavelength. As a result, there is a problem in which a cost of the exposure optical system becomes high and production cost of the hologram screen is increased. Further, although it is necessary to arrange balance of each intensity of the red, green and blue laser lights, it is very difficult to perform this arrangement, and a lot of time is required in the manufacturing process.
Further, in this method, since the red, green and blue laser lights are used for exposing the photosensitive material, it is very difficult to arrange characteristic balance (i.e., RGB balance) between hologram elements each of which is recorded by the red, green and blue laser lights. As a result, strong unevenness of color partially occurs on the hologram screen so that color of the image, which is reproduced on the hologram screen, becomes worse.
Still further, in the above hologram element, three kinds of light diffusion bodies are recorded by the red, green and blue laser lights. As a result, an external light is easily diffracted and scattered in this hologram screen so that the hologram element becomes cloudy. The transparency becomes worse on the cloudy hologram element so that appearance also becomes worse.
The third aspect of the present invention aims to solve the above problems. That is, the third invention has superior color reappearance on the hologram screen. Further, when producing the hologram element which forms the hologram screen, it is possible to utilize either a single laser light, or two color (red and green) laser lights. Still further, it is possible to provide the hologram screen having a low producing cost and a simplified producing process, as explained in detail below.
According to the invention, the image light, which is irradiated from the image projector, is scattered and diffused on the hologram screen so that the output light is obtained and the image is reproduced on the hologram screen.
The method of producing the hologram element is characterized in that the half bandwidth of the hologram spectrum is 100 nm or more, and the diffusion light obtained by the light diffusion body in which the light diffusion angle is large, is used as the object light, and the non-diffusion light is used as the reference light; and both lights are irradiated on to the photosensitive material in order to form the interference fringe thereon.
The hologram spectrum is defined as the intensity (i.e., efficiency) for each wavelength of the output light which is scattered and diffused on the hologram screen (see FIGS. 53 and 61). The abscissa is the wavelength, and the ordinate is the efficiency. Further, the efficient is a ratio of the intensity of the output light and the intensity of the incident light.
As shown in
As mentioned above, in the third aspect of the present invention, the half bandwidth of the hologram spectrum is 100 nm or more. Accordingly, it is possible to obtain the output light by scattering and diffusing without emphasis of the particular wavelength of the image light, and to obtain the hologram screen which can reappear clearly the color tone of the image light (see FIGS. 62 and 63).
Further, as mentioned above, the object light is prepared by the light diffusion body in which the light diffusion angle is large, the scattering extent becomes large. Since the object light is irradiated, the half bandwidth of the hologram spectrum of the hologram element becomes 100 nm or more (see FIGS. 57 and 58).
Further, since the hologram element is prepared by the laser light having the monochrome or two colors (i.e., red and green), there is no problem mentioned in the conventional art. That is, since the hologram element is prepared by using the exposure optical system having the laser oscillator which can generate the laser light having the single color or two colors, it is possible to realize low producing cost. Further, since it is not necessary to arrange the intensity balance of three laser lights each having different wavelength, it is possible to realize easy production. Further, since the hologram element is prepared by the laser light having the monochrome or two colors, there is no scattering and diffusion due to the external light and no cloudiness on the hologram screen so that it is superior in the transparency.
In the third aspect of the present invention, since the hologram element is transparent, the observer can see through the back of the hologram screen when the image is reproduced. Accordingly, it is very effective to utilize the hologram screen of the third aspect of the present invention as the advertising board in the shopping center, or as the ticket window. When the image light is not irradiated on the hologram screen, the hologram screen is merely transparent plate so that there is no influence for the view field.
On the other hand, when the half bandwidth of the hologram screen is 100 nm or less, since the output light is emphasized for the particular wavelength band, the color reappearance of the image light may become worse. Since the half bandwidth becomes large, the hologram spectrum becomes flat and the color reappearance of the image light is improved. However, since a human eye can recognize only visible ray, it is sufficient to set the half bandwidth to approximately 400 nm.
As the light diffusion body in which the light diffusion angle is large, it is possible to utilize a double-faced ground glass, an one-faced ground glass, and an opal glass. Further, as a method for enlarging the light diffusion angle of the light diffusion body, for example, there is the method for enlarging the light diffusion angle by laminating a plurality of light diffusion bodies. Further, there is the method for changing the scattering characteristic of the light diffusion body itself by changing the material of the light diffusion body, or providing the surface process on the light diffusion body. Still further, it is possible to realize the large light diffusion angle by combining lens array. In this case, by partially changing the f-value of the lens, it is possible to partially change the scattering characteristic of the light diffusion body, and to obtain the good scattering characteristic.
The above light diffusion angle will be explained in detail below. The scattering light is generated by irradiating the laser light perpendicularly to the light diffusion body. At that time, when the intensity of the laser light which transmitted perpendicularly to the light diffusion body is set to 100, the efficiency of the scattering light for each output angle is measured. In this case, the output angle at the efficiency of 50% is the light diffusion angle (see the first embodiment).
According to the invention, the light diffusion angle is preferable at the time when the light diffusion angle of the hologram screen is 10°C or more. In this angle, it is possible to obtain the hologram screen having superior reappearance. When the light diffusion angle of the hologram screen is 10°C or less, the scattering extent of the object light becomes small, it is difficult to obtain the hologram element having the half bandwidth mentioned above. Further, although the color reappearance becomes good when the light diffusion angle of the light diffusion body becomes large, the brightness of the image becomes worse so that it is difficult to watch the image. Accordingly, it is preferable to set the upper limit of the light diffusion angle to the angle 60°C. Still further, when the hologram screen shown in
According to the invention, the half bandwidth of the hologram spectrum is 100 nm or more. The diffusion light obtained by the light diffusion body is used as the object light, and the non-diffusion light is used as the reference light. The object light and the reference light are irradiated on the photosensitive material having the thickness of 1 to 20 μm in order to from the interference fringe on the hologram element. Accordingly, it is possible to obtain the scattered and diffused output light without emphasis of the particular wavelength of the image light. As a result, it is possible to realize the hologram screen which can preferably represent the color tone of the image.
As shown in
Since the above mentioned hologram element can be produced by using laser light having the monochrome or two colors, it is possible to obtain the hologram screen having the following features, i.e., low producing cost, simplified producing processes, and high transparency.
On the other hand, when the thickness of the photosensitive material is 1 μm or less, the image becomes very dark since the efficiency of the hologram element is too low so that the observation of the image becomes very difficult. Further, when the thickness of the photosensitive material is 20 μm or more, the half bandwidth is 100 nm or less so that the color at the particular wavelength becomes strong and the color reappearance becomes worse.
According to the invention, the peak wavelength of the hologram spectrum is either 525 nm or less, or 585 nm or more. Further, the half bandwidth of the hologram spectrum is 100 nm or more. After the interference fringe was formed on the photosensitive material, the hologram element is produced by adjusting the refractive index of the photosensitive material.
On the other hand, there is a wavelength dependency in the sensitivity of the human eye (a relative luminosity factor (i.e., a sensitivity of a human eye)) as shown in FIG. 68. That is, as shown in
In the third aspect of the present invention, the peak wavelength of the hologram spectrum is either 525 nm or less, or 585 nm or more. The spectral luminous efficiency at these wavelengths are 80% for the sensitivity at the peak wavelength, i.e., 555 nm. Accordingly, it is possible to obtain the hologram screen which can reappear the original color tone of the image light without the particular wavelength on the image light.
That is, an amount of change of the refractive index of the photosensitive material is controlled by adjusting the process conditions from before exposure of the photosensitive material until after production of the hologram screen, and it is possible to realize the hologram screen having good color-reappearance.
In the case of a volume phase type hologram which records the interference fringe by utilizing a refractive index modulation of the photosensitive material, although the extent of the amount of change of the refractive index is slightly changed depending on the photosensitive material to be used, the above extent is strongly depended to the exposure conditions and the process conditions before and after the exposure.
According to the Bragg's formula,
Where, "n" is a refractive index of the photosensitive material, "d" is a pitch of the interference fringe, θ is a half of an intersected angle of the reference light and the object light, and λ is a recorded wavelength.
The pitch "d" of the interference fringe is determined at the exposure, and the amount of change Δn of the refractive index is determined after completion of all processes. The reproduced wavelength λ' at the reproduction of the hologram element can be expressed by the following formula.
As is obvious from the formula (9), when the amount of change Δn of the refractive index becomes large, the reproduced wavelength λ' becomes long. As mentioned above, it is possible to obtain a desired peak wavelength by suitably determining the amount of change Δn.
Further, a diffractive efficiency η is also changed depending on the amount of change Δn. When the hologram is the phase and transmittion-type hologram, the following formula is given theoretically.
As is obvious from the above formula, the diffractive efficiency η is influenced by the amount of change Δn.
Further, there is a feature in which the diffractive efficiency η is changed sinusoidally. In this case, however, since the above formula is given for a simple lattice (i.e., the hologram is formed by one reference light and one object light), the above formula becomes more complicated when there are a plurality of object lights according to the present invention.
The hologram spectrum is formed as shown in FIG. 84. When there are a plurality of object lights according to the present invention, one inclined interference fringe (i.e., a diffraction lattice) is formed for one object light (i.e., an object light having one direction). That is, it is possible to form the interference fringe which has different inclinations (i.e., diffraction lattice) depending on the irradiated direction of the object light at the location on the light diffusion body. The difference of the wavelength occurs depending on the difference of inclination when reproducing the white light.
The difference of the wavelength is shown by the solid lines in FIG. 84. The diffraction efficiency η is also changed depending on the reproduced wavelength λc. Accordingly, the efficiency is different due to the reproduced wavelength as shown in FIG. 78. As a result, the hologram spectrum on the hologram screen is formed as shown by dotted line in
As mentioned above, by changing the amount of change Δn of the refractive index of the photosensitive material after completion of all processes, it is possible to change not only the reproduced wavelength, but also the half bandwidth. As a result, by suitably adjusting the amount of change Δn of the refractive index, it is possible to adjust the peak wavelength at the hologram spectrum to either 525 nm or less, or 585 nm or more, and to adjust the half bandwidth to 100 nm or more. Further, it is possible to adjust the half bandwidth based on the exposure intensity, the intensity ratio of the reference light and the object light (R/O), and the heat conditions after exposure.
According to the invention, after completion of the interference fringe, the heating process is provided to the photosensitive material in the range of 80°C to 150°C. There are some kinds of photosensitive materials in which the refractive index can be adjusted by the heating process after exposure and the efficiency of the hologram element is increased. The amount of change Δn of the refractive index is changed based on the heating conditions.
When the heating process is performed, as is obvious from the formula (9), the peak wavelength at the hologram spectrum can be adjusted to 525 nm or less, or 585 nm or more, and the half bandwidth can be adjusted to 100 nm or more. In this case, when the temperature at the heating process is 80°C C. or less, the image becomes dark so that it is difficult to observe the image. On the other hand, when the temperature exceeds 150°C C., and when a film is used as the photosensitive material, the film may be deformed. Further, the color of the image may be worse due to color of the photosensitive material itself.
Further, it is preferable to set the continuous heating time in the range of 1 minute to 10 hours. When the heating time is 1 minute or less, the efficiency may be worse. On the other hand, when the heating time exceeds 10 hours, deformation and color may occur in the photosensitive material, and productivity of the hologram screen becomes worse.
Still further, the optimum temperature for the heating process is different in accordance with kinds of photosensitive material to be used. For example, as shown in
Further, the heating method is performed within a oven so as not to contact the photosensitive material (front and back surfaces) to other parts during the heating. If the photosensitive material contacts to other parts, the difference in thermal conductivity occurs between these parts so that unevenness of color brightness occur when reproducing the image.
According to the invention, a sum of an exposure intensity of the object light and the exposure intensity of the reference light is set within 0.02 to 50 mW/cm2, and the object light and reference light are irradiated onto the photosensitive material to form the interference fringe in order to provide the hologram element.
As mentioned in the formula (8), the reproduced wavelength is changed in accordance with the amount of change Δn of the refractive index which can be changed by the exposure intensity.
For example, in the case of the polymer made by Dupont Co., ltd., as disclosed in the document "Holographic transmission elements using improved photopolymerfilms " by William J. Gambogi et al., SPIE Vol. 1555, Computer and Optically Generated Holographic Optics (Fourth in a Series), 1991, pp 256-267, when the exposure intensity becomes weak, the amount of change Δn of the refractive index becomes large after completion of all processes.
Accordingly, when the exposure intensity becomes weak, the reproduced wavelength λ' becomes long. On the other hand, when the exposure intensity becomes strong, the reproduced wavelength λ' becomes short. As mentioned above, since it is possible to change the reproduced wavelength by changing the exposure intensity, it is possible to adjust the peak wavelength at the hologram spectrum to either 525 nm or less, or 585 nm or more, by suitably adjusting the exposure intensity. Further, based on the formula (10), it is possible to adjust the half bandwidth so as to become 100 nm or more.
When the sum of the exposure intensity is 0.02 mW/cm2 or less, there are problems in which the intensity becomes very weak, and the exposure time becomes very long, so that unevenness of color may be occur on the hologram screen. On the other hand, when the sum of the exposure intensity is 50 mW/cm2 or more, there are problems in which the peak wavelength becomes very short, and the half bandwidth becomes very narrow, so that the color of the reproduced image becomes considerably worse.
When the exposure intensity is constant, it is possible to change the peak wavelength and the half bandwidth at the hologram spectrum in accordance with the intensity ratio (R/O) of the object light and the reference light. That is, as, the intensity ratio of the object light (O) and the reference light (R) is set to 0.1 to 30, and the object light and the reference light are irradiated onto the photosensitive material in order to form the interference fringe. As is obvious in
When the intensity ratio R/O is 0.1 or less, the transparency of the hologram screen becomes worse. However, when there is no problem if the transparency becomes worse, it is possible to set the intensity ratio R/O to a small value in the range in which the hologram efficiency is not decreased. In this case, the half bandwidth becomes wide, and the color reappearance becomes very good. Further, when the intensity R/O is larger than 30, the half bandwidth becomes small and the color reappearance becomes worse.
According to the invention, the peak wavelength of the hologram spectrum is either 525 nm or less, or 585 nm or more. The hologram element is produced by adjusting the thickness of the photosensitive material after completion of the interference fringe.
When the thickness of the photosensitive material is changed from the thickness at the exposure after completion of all processes, the pitch "d" of the interference fringe is also changed after completion of all processes. When the amount of change is given to Δd, the reproduced wavelength λ' is given by the formula (1) as follows when the hologram is reproduced.
Accordingly, if the thickness of the photosensitive material after completion of all processes is larger than the thickness at the exposure, the reproduced wavelength λ' becomes long. On the other hand, if the thickness of the photosensitive material after completion of all processes is smaller than the thickness at the exposure, the reproduced wavelength λ' becomes short.
According to the invention, the peak wavelength of the hologram screen is either 525 nm or less, or 585 nm or more, in order to avoid the peak wavelength for the relative luminosity factor. Further, the reference light and the image light are irradiated onto the photosensitive material to form the interference fringe in such a way that the incident angle θr of the reference light on the photosensitive material is different from the incident angle θe of the image light on the hologram screen. As a result, it is possible to reproduce the image light with superior color tone without emphasis of the particular wavelength of the image light.
In this case, the reproduced wavelength λc is given by the following formula (5).
Where, "n" and "d" are not changed after exposure and after production of the hologram element. Accordingly, when the incident angle θe of the image light onto the hologram screen is larger than the incident angle θr of the reference light, the reproduced wavelength λc becomes shorter than the recorded wavelength. On the other hand, when the incident angle θe of the image light onto the hologram screen is smaller than the incident angle θr of the reference light, the reproduced wavelength λc is shifted to the wavelength which is longer than the recorded wavelength (see FIG. 22). As a result, it is possible to obtain the hologram element having the peak wavelength of either 525 nm or less, or 585 nm or more.
According to the invention, it is preferable that an amount of angle correction, which is the difference between the incident angle θr of the reference light and the incident angle θe of the image light, is in the range of -5°C to +5°C. As a result, it is possible to obtain the hologram screen having the superior color reappearance. When the amount of angle correction is out of the above range, there is a problem in which the efficiency of the hologram is decreased, and the image becomes dark.
According to the invention, the half bandwidth of the hologram spectrum is 100 nm or more. As a result, it is possible to obtain the scattered and diffused output light without emphasis of the particular wavelength of the image light. As a result, it is possible to obtain the same effect as the case which enlarges the scattering extent of the object light, and the half bandwidth of the hologram spectrum becomes 100 nm or more.
The preferred embodiments of the third aspect of the present invention will be explained in detail below.
The first embodiment is explained in detail with reference to
As shown in
As shown in
The image light 331 from the image projector 33 is scattered and diffused on the hologram screen 31 so that it is possible to obtain the output light 332. As a result, the observer 35 can observe the reproduced image on the hologram screen 31. Since the hologram element is formed by the transparent material, it is possible to transmit the back light 333 of the background 37 which is arranged opposite to the observer 35. Accordingly, the observer can observe the background 37 with the image on the hologram screen 31. In this case, the image projector 33 may be arranged to the location lower than the observer 35 in the opposite side of the observer 35. On the other hand, it is possible to form the hologram screen by using the reflection type hologram element.
In the exposure optical system 310 shown in
The object light 3117 and the reference light 3118 are irradiated on the photosensitive material 3120 (i.e., the photopolymer plate made by Dupont Co.) which is bonded on the glass plate 3123, and the interference fringe formed by these lights is recorded on the photosensitive material 3120. As a result, it is possible to obtain the hologram element in which the light diffusion body 3116 is recorded on the photosensitive material 3120.
When the image light is irradiated on the hologram element, the light diffusion body 3116 is reproduced. Accordingly, when irradiating the image light on the hologram element, the image light is scattered and diffused so that the image light becomes the output light, as well as the diffusion light output from the light diffusion body 3116.
The performance evaluation of the hologram screen according to the third embodiment will be explained in detail below. In this case, when producing the hologram element, the number of the double-faced ground glass, which forms the light diffusion body 3116, was changed in order to change the scattering characteristic of the light diffusion body 3116. In
That is, the laser light is irradiated perpendicular onto the surface of the double-faced ground glass so as to obtain the diffusion light, the intensity ratio of the diffusion light for each output angle was measured. In measurement of the intensity, the intensity of the diffusion light was set to "100" when the output angle was 0°C (i.e., the direction perpendicular to the surface of the light diffusion body). As is obvious from the drawing, when the number of the double-faced ground glass is increased, it is possible to obtain the diffusion body having the large scattering extent.
In this case, the light diffusion angle of the light diffusion body means the output light in which the intensity ratio of the scattering light becomes 50. Accordingly, as shown in
Next, in the exposure system shown in
The measuring method of the hologram spectrum will be explained below. In
Further, in the above producing method, the hologram elements each having the half bandwidth of 60, 80, 100, 120, 140, 160 and 180 nm were made by suitably changing kinds, the number and other producing conditions, of the double-faced ground glass. The above hologram screens were provided in the display apparatus, and the image light was irradiated from the image projector in order to reproduce the image.
The image on the hologram screen was observed by sixteen observers, and the evaluation was performed by the observers in accordance with the following seven grades regarding the color tone of the image. In this case, the seven grades of the evaluation are as follows.
GRADE 7→very good color tone, and natural color;
GRADE 6→good color tone, and no feeling of difference;
GRADE 5→slightly different color tone, but no feeling of difference;
GRADE 4→either of them;
GRADE 3→different color tone, and slight feeling of difference;
GRADE 2→different color tone, and feeling of difference; and
GRADE 1→entirely different color tone, and feeling of difference.
The result of the evaluation is shown in
As shown in
As shown in
The operation of the third aspect of the present invention will be explained in detail blow. The hologram spectrum of the hologram element is shown in FIG. 61. As shown in
In the hologram screen in this embodiment, the half bandwidth of the hologram element is 100 nm or more. Accordingly, it is possible to obtain the scattered and diffused output light without emphasis of the particular wavelength of the image light, and to obtain the hologram screen which can reappear the good color tone of the image light (see FIGS. 62 and 63).
The object light and the reference light are irradiated onto the photosensitive material having the thickness of 1 to 20 μm (for example, the photopolymer made by Dupont Co. Ltd. was used.) in order to form the interference fringe on the hologram element. The half bandwidth of the hologram element is 100 nm or more. The light diffusion body is formed by laminating three double-faced ground glasses. Further, the intensity ratio R/O of the reference light and the object light at the center of the photosensitive material is 3, and the incident angle θr of the reference light on the photosensitive material (see
The half bandwidth and peak efficiency of the hologram element, which were prepared in accordance with the above conditions, were measured based on the method of the first embodiment. The result of measurement is shown in
In the third embodiment, the intensity ratio R/O of the reference light (R) and the object light (O) is set to 0.1 to 30, and the reference light and the object light are irradiated on the photosensitive material in order to form the interference fringe on the hologram element. In this case, the half bandwidth of the hologram spectrum is 100 nm or more. The light diffusion body is formed by laminating four double-faced ground glasses. The intensity ratio R/O of the reference light and the object light is 3, and the incident angle θr and the incident angle θe are 30°C. As shown in
In this embodiment, the peak wavelength of the hologram spectrum is either 525 nm or less, or 585 nm or more. The thickness of the photosensitive material (for example, the photopolymer made by Dupont Co.) is 6 μm. The light diffusion body is formed by laminating three double-faced ground glasses, and the intensity ratio R/O of the reference light and the object light is 0.8, 3 and 5. Further, the incident angle θr and the incident angle θe are 30°C.
As shown in
Even if the intensity ratio R/O is in the range of 0.1 to 30, there is the case that the peak wavelength becomes out of extent. In
Accordingly, although the intensity ratio R/O is changed in order to set the peak wavelength within the above extent for every change of conditions of the hologram production, when the intensity ratio R/O is adjusted in the range of 0.1 to 30, it is possible to set the peak wavelength to either 525 nm or less, or 585 nm or more.
Further, there is a wavelength dependency in the sensitivity of a human eye. Accordingly, in the display apparatus shown in
The hologram spectrum which was multiplied by the spectral luminous efficiency is shown in FIG. 69. Since the human spectral luminous efficiency has the large peak at the wavelength of 555 nm, the large peak occurs in the vicinity of the wavelength of 555 nm as shown in FIG. 69.
When the image light is reproduced by using the hologram screen in which the intensity ratio R/O is 1 and the peak wavelength is 547 nm as shown in
The image is reproduced by using the hologram screen having the hologram spectrum shown in
Accordingly, when providing the hologram screen formed by the hologram spectrum having the peak wavelength at the wavelength of either 525 nm or less, or 585 nm or more and avoiding the peak wavelength of the spectral luminous efficiency, it is possible to provide good appearance of color tone of the original image without emphasis of the particular wavelength of the image light, and to realize the hologram element having superior color reappearance.
In this embodiment, the incident angle θr of the reference light on the photosensitive material is different from the incident angle θe of the image light on the hologram screen, and the reference light and the object light are irradiated on the photosensitive material in order to form the interference fringe. The peak wavelength of the hologram spectrum is either 525 nm or less, or 585 nm or more. In this case, the thickness of the photosensitive material (for example, the photopolymer made by Dupont Co. Ltd.) is 6 μm, and the light diffusion body is formed by laminating three double-faced ground glass. Further, the intensity ratio R/O of the reference light and the object light is set to 3.
The hologram screen having the angle 40°C as the incident angle θe of the image light was prepared. In this case, the incident angle θr of the reference light was changed by 40°C, 41°C, 42°C and 43°C. That is, the amount of the angle correction (i.e., θr-θe) was determined as 0°C, 1°C, 2°C and 3°C. The relationship between the peak efficiency and the amount of the angle correction is shown in FIG. 74. As shown in
As mentioned above, by changing the incident angle θr of the reference light and the incident angle θe of the reproduced light, the peak wavelength of the hologram spectrum can be set to either 525 nm or less, or 585 nm or more. Since the hologram element according to this embodiment is slipped from the peak of the spectral luminous efficiency, it is possible to realize good color reappearance of the image.
In this embodiment, a plurality of object lights each of which have different angle are irradiated onto the photosensitive material in order to form the interference fringe. Further, the half bandwidth of the hologram spectrum is 100 nm or more.
AS shown in
The scattering extent of the object light was measured by the following method. That is, as shown in
The result of measurement is shown in FIG. 77. The curve indicated by the mark "Δ" is in the case that only parallel light 3115 was irradiated onto the light diffusion body 3116, and the curve indicated by the mark "□" is in the case that the parallel light 3115 and the divergence light 3130 were irradiated onto the light diffusion body 3116.
As is obvious from the drawing, it is possible to improve the scattering extent of the object light by adding the divergence light 3130 to the parallel light 3115. When the scattering extent of the object light is increased, it is possible to produce the hologram element having board peak wavelength so that it is possible to obtain the hologram element having good color reappearance.
In this embodiment, a sum of the exposure intensity of the intensity of the object light and the intensity of the reference light was determined in the range of 0.02 to 50 mw/cm2, and the object light and the reference light were irradiated on the photosensitive material in order to form the interference fringe on the hologram element. The thickness of the photosensitive material, for example, photopolymer, was 6 μm, and the light diffusion body was formed by three double-faced ground glass. The intensity ratio of the reference light and the object light was 4. The incident angle θr of the reference light on the photosensitive material and the incident angle θe of the image light on the hologram screen were 35°C. The amount of exposure was 20 mJ/cm2.
As shown in
In this embodiment, it is possible to set the peak wavelength at the hologram spectrum to either 525 nm or less, or 585 nm or more, and to set the half bandwidth to 100 nm or more, by adjusting the sum of the exposure intensity in the range of 0.02 to 50 mW/cm2.
In this embodiment, after completion of the interference fringe, the ultraviolet light (UV light) having the intensity 0.1 mw/cm2 was irradiated onto the photosensitive material, and the heating conditions was adjusted in the range of 80 to 1500 in order to form the hologram element. In this case, the peak wavelength is either 525 nm or less, or 585 nm or more, and the half bandwidth is 100 nm or more.
Further, the thickness of the photosensitive material (the photopolymer was used) was 6 μm and 10 μm. The light diffusion body was formed by three laminated double-faced ground glass, and the intensity ratio R/O of the reference light and the object light was 5. Further, the incident angle θr of the reference light and the incident angle θe were 30°C, and the amount of exposure was 20 mJ/cm2. The result of measurement is shown in
As shown in
In this embodiment, after completion of the interference fringe, the hologram element was produced in accordance with the following conditions. That is, the hologram element was irradiated by the ultraviolet having the intensity of 0.1 mW/cm2, and heated by 120°C during one hour. As shown in
In this case, since the hologram element is heated and pressed, the photopolymer becomes soft. Further, after exposure or irradiation of the UV, the hologram element can be pressed. In this case, it is possible to set a low heating temperature. Further, when the dichromated gelatin (DCG) is used as the photosensitive material, the following adjustments are performed. That is, when the peak wavelength is shifted to the long wavelength, a dry plate coated by the DCG before exposure, is exposed after vacuum process in the range of 0.1 to 1 (Torr) and from 10 seconds to 2 hours.
When the Ar laser having the wavelength 514 nm is used, the wavelength was shifted to the long wavelength by 550 nm in the conditions of 0.2 Torr and 10 minutes, and by 590 nm in the conditions of 0.2 Torr and 1.5 hours. When the peak wavelength is shifted to the short wavelength, the thickness of the photosensitive material becomes more thick than the thickness at the exposure by performing a chemical hard-film process after swelling of the hologram in warm water during development. As a result, it is possible to shift the peak wavelength to the short wavelength. In this case, after swelling of the hologram in the warm water of 30°C C. and during five minutes, and after swelling it in a rapid fixer during five minutes with 25°C C., the peak wavelength was shifted to the 480 nm.
Before describing the preferred embodiments, a conventional art and its problem are explained below. There is a known transparent hologram screen which can reproduce the image based on the output light by scattering and diffusing the image light from the image projector. The observer can observe the reproduced image on the hologram screen and can see the background through the hologram screen. This type of the hologram screen can be utilized, for example, in the ticket window in a bank or hospital, as mentioned above. Further, the hologram screen can be utilized as an advertising board in a shopping center, and as a head-up display apparatus.
One example of a display apparatus using the transmission type hologram screen is shown in FIG. 110. The image projector 412 is arranged at the back of the hologram screen 49, i.e., opposite to the observer 48. The image light 4120 is irradiated from the image projector 412 onto the hologram screen 49 so that the image is reproduced on the hologram screen 49 and the image can be observed by the observer 48.
On the other hand, a display apparatus using the reflection type hologram screen is shown in FIG. 111. The image projector 412 is arranged at the front of the hologram screen 490, i.e., at the same side as the observer 48. The image light 4120 from the image projector 412 is irradiated in order to reproduce the image on the hologram screen 490. As shown in
In this case, as shown in
There is, however, a problem in which cloudiness occurs on the hologram screen because the interference fringe formed by the object light is recorded thereon. When cloudiness occurs on the screen, it is very difficult to observe the background through the hologram screen. Particularly, when there is no image on the hologram screen, the observer feels difference of the image at the background due to this cloudiness.
A method of producing the hologram screen having wide view angle has been disclosed, for example, in the Japanese Unexamined Patent Publication No. 9-127853. According to this method, the diffusion light, i.e., the object light, is obtained by irradiating a plurality of lights, each of which has different direction, onto the light diffusion body. On the other hand, the non-diffusion light is used as the reference light. The object light and the reference light are irradiated on the photosensitive material in order to form the interference fringe. Further, two kinds or more, each having different diffusion angle, of the light diffusion bodies are bonded so as to form one light diffusion body. Then, the object light and the reference light are irradiated on the photosensitive material in order to obtain the hologram screen. According to this method, since it is possible to use the diffusion light in which the difference in intensity due to scattering direction is small, it is possible to obtain the hologram screen having wide view angle.
On the other hand, since there is a proper feature in which the observer can observe the image from only particular range (a view angle) on the hologram screen. Accordingly, the hologram screen having wide view angle has high utility in various fields. However, when the view angle becomes broad, cloudiness is increased on the hologram screen.
As another method, a method for preventing cloudiness from the image has been disclosed in the Japanese Patent Unexamined Publication No. 9-127612.
It is assumed that the reference light is not irradiated, and only object light is irradiated on the photosensitive material to expose it. When the efficiency ηOO of the hologram screen obtained by the above conditions is 5% or less, the intensity of the object light is given as A. The photosensitive material is exposed by using the object light and the reference light having the intensity which corresponds to the intensity A. As a result, it is possible to obtain the hologram screen having no cloudiness on the image.
There is a problem, however, in the above method. That is, even if the exposure is performed by the object light which exceeds the efficiency ηOO of 5%, there is possibility in which no cloudiness is obtained on the hologram screen. Accordingly, the above conventional method has been yet insufficient in order to solve cloudiness on the hologram screen.
Further, the hologram screen using the dichromated gelatin (DCG) as the photosensitive material has been disclosed in the above Japanese Unexamined Patent Publication No. 9-127612. In this case, it is necessary to provide a wet development process in the producing process using the DCG. Accordingly, when the DCG becomes hard in the development process, small cracks occur in the DCG so that the hologram screen becomes cloudy.
The inventors found the fact that, if there is no cloudiness on the hologram screen, the observer does not mind a cloudy state even if the efficiency ηOO becomes large. On the other hand, since the hologram screen made by the DCG frequently becomes cloudy, it is necessary to set the efficiency ηOO to 5% or less.
The fourth aspect of the present invention aims to solve the above problems, and to provide the hologram screen which has superior transparency and no cloudiness, and can observe clearly the background by the observer. Further, a producing method of the hologram screen is provided.
According to the invention, the image light from the image projector is scattered and diffused to obtain the output light so that the image can be reproduced on the screen, and the hologram screen is characterized by a haze ratio of 5 to 60%.
As mentioned above, the hologram screen according the fourth aspect of the present invention has the haze ratio of 5 to 60%. Since the haze ratio is set in the range of 5 to 60%, the light which is input from the external, except for the image projector, to the hologram screen has the low scattering extent, it is possible to output the image with high efficiency. Accordingly, when the observer observes the hologram screen, there is no cloudiness of the hologram screen due to the external light, and it is possible to transmit the background without cloudiness, and to clearly observe the background through the hologram screen. That is, the observer can observe the back at the same time the image reproduced on the hologram screen, different from the non-transparent hologram. As a result, this transparent hologram can be utilized as, for example, the advertising board in the shopping center. Further, the transparent hologram screen can be utilized as a head-mount display of a mobile system.
When the haze ratio exceeds 60%, there is cloudiness on the hologram screen so that it is difficult to clearly observe the back. On the other hand, when the haze ratio is 5% or less, the efficiency of the hologram screen becomes low so that the image becomes dark.
In general, a haze ratio which indicates cloudiness of a transparent plate has been defined, for example, in the JIS-K7105 (Japanese Industrial Standard), and this is used in the present invention. In the case of the hologram screen, even if the haze ratio becomes high, the observer can clearly observe the back, i.e., the hologram screen has high transparency.
The haze ratio can be expressed as follows.
Where, H is a haze ratio (%), Td is a diffused transmission (%), and Tt is an all lights transmission (%). Concretely, Tt is the light intensity which is transmitted perpendicularly to the center of the light diffusion body or the hologram screen (precisely, the light intensity of the scattering light in the range of ±3.5°C), and Td is the total intensity of the scattering light at all directions except for the center direction.
The cause of cloudiness of the hologram screen will be explained compared to cloudiness of the light diffusion body.
In the general light diffusion body, the incident light is scattered due to unevenness of the surface, or due to particles existing within the diffusion body and scattering the light. As shown in
When the haze ratio becomes small, the bending extent of the lights 4731 and 4732 becomes small. However, except that the bending extent is extremely small, the obscuration of the object 470 always occurs when the observer 48 observes the image. For example, when the beam of lights 4731 and 4732 are bent by 0.1°C, there is the difference of 3.5 mm at the observer location which is apart from the light scattering body 472 by the distance of 2 m. Further, there is the difference of 8.7 mm at the observer location which is apart from the light scattering body 472 by the distance of 5 m. In general, since a diameter of the pupil of human eye is approximately 5 mm, the beam of lights 4731 and 4732 are bent by only 0.1°C, the obscuration of the object 470 occurs at the location of the observer 48.
On the other hand, the hologram screen, as mentioned below, the diffusion body which is formed by transmitting the laser light through the light diffusion body or reflecting the laser light therefrom is used as the object light, and the non-diffusion light is used as the reference light. The interference fringe is formed by the object light and the reference light, and recorded as the difference in the refractive index of the material of the photosensitive material. The recorded interference fringe functions as the diffractive lattice. In general, the material of the hologram screen is transparent, and the surface thereof is flat.
As shown in
In this case, a part of the beam of light 471 is diffracted by the interference fringe 4100 and output from the hologram screen 41 as the beam of light 475. Since the incident direction of the beam of light 474 is different from the incident direction of the image light, the intensity of the beam of light 475 becomes low compared to the beam of light 474. However, since there are many interference fringes 4100, the beam of light 475 may become the light having a certain grade of the intensity. When the intensity of the beam of light 475 becomes strong due to efficiency and number of the interference fringe 4100, the haze ratio of the hologram screen 41 becomes high.
However, the beam of light 474 which is not diffracted (see
On the other hand, cloudiness which causes non-transparency of the hologram screen, occurs due to the fact that the external light is diffracted by the normal interference fringe (i.e., interference fringe formed by the object light and reference light) and another interference fringe formed by two object lights (i.e., unnecessary interference fringe), and the diffracted light is output to the direction of the observer's view line. In this case, the external light indicates the lights which are input to the hologram screen, except for the image light irradiated to the hologram screen and the object light from the back of the hologram screen.
In the interference fringe 100, the interference fringe 101 is recorded by the reference light 4310 and the object light 4321, the interference fringe 102 is recorded by the reference light 4310 and the object light 4322, and the interference fringe 103 is recorded by the reference light 4310 and the object light 4323, as shown in FIG. 106. Accordingly, in the interference fringe 100, the image light which was input from the same direction as the reference light 4310 can be effectively diffracted, but the lights which are input from other directions cannot be effectively diffracted. Further, as shown in
As shown in
As mentioned above, when the external light is diffracted by the normal interference fringe and another interference fringe due to "Fresnel noise", and output to the direction of the observer's view line, the observer feels cloudiness of the hologram screen. That is, the cloudiness of the hologram screen is caused by a cloudy state of the whole of the surface of the hologram screen when the external light is diffracted by the interference fringe and output to the direction of the observer's view line. That is, cloudiness is not caused by the scattering of the background light. Even if the scattering extent of the background light lies in a certain high grade, i.e., even if the haze ratio is high, cloudiness of the hologram is not observed by the observer when the intensity of the external light which is diffracted to the observer is weak. As mentioned above, in the case of cloudiness of the hologram screen, even if the haze ratio is high, the cloudiness extent which is observed by the observer is small and different from cloudiness of the normal light scattering body.
The result of comparison of the hologram screen and the normal light scattering body is explained below. The scattering characteristic (i.e., an intensity distribution for each output angle of the output light) of the transmission light of the hologram screen having the haze ratio of 30% and the light diffusion body having the haze ratio of 5% (for example, an anti-glare film AG-30 made by NITTO DENKO Co., Ltd.) is shown in FIG. 108. The hologram screen used in this embodiment was made based on a method explained in the following second embodiment.
As shown in
According to the invention, it is preferable that a screen gain of the hologram screen is 0.3 or more. As a result, it is possible to obtain the hologram screen in which the brightness of the image on the hologram screen is not reduced. Accordingly, it is possible to obtain the hologram screen having the clear and superior image.
When the hologram screen is arranged into a popular room, the back brightness of the hologram screen becomes 400 cd/m2. Accordingly, it is necessary to provide the brightness exceeding the above in the brightness of the image which is imaged on the hologram screen (see FIG. 85).
On the other hand, a high brightness type image projector (for example, a liquid crystal projector) which is available in the market has a minimum projecting display size of 40 inches. Further, it has been known that the maximum illuminance of the image projected on this display size is approximately 4000 lux. Further, in general, the screen gain can be obtained based on the following formula.
Accordingly, the screen gain which becomes the illuminance of 4000 (lux) and the brightness of 400 (cd/m2) is approximately 0.3. As mentioned above, it is necessary to set the screen gain to 0.3 or more in order not to reduce the brightness of the image on the hologram screen. If the screen gain is 0.3 or less, the image on the hologram screen becomes dark, and it may be difficult to distinguish from the back of the hologram screen. In this case, the upper limit of the screen gain must be determined so as not to exceed the haze ratio of 60% since the haze ratio is increased in accordance with increase of the screen gain. Accordingly, the screen gain cannot be determined uniformly since it is dependent on the characteristic of the hologram screen.
According to the invention, in the transmission type or reflection type hologram screen, the intensity ratio ER/EO of the intensity EO of the object light and the intensity ER of the reference light is changed in accordance with the scattering angle of the light diffusion body. In this case, the scattering angle of the light diffusion body is an angle determined when the intensity ratio Iθ/IO is 0.5. Where, the intensity IO is defined by the light intensity which is output perpendicularly (i.e., direction of angle 0°C) from the light diffusion body, and the intensity Iθ is defined by the light intensity which is output to the direction of angle 0°C) from the light diffusion body.
As shown in
Accordingly, when the scattering angle of the light diffusion body is changed, it is necessary to change the intensity IθO in order not to decrease the efficiency ηRO. In this case, to change the intensity IθO means the change of the intensity EO., i.e., the intensity ratio ER/EO. If the efficiency ηRO becomes low, the reduced image becomes dark.
Further, even if the intensity ratio ER/EO is constant, the efficiency of the "Fresnel noise" which is formed by the interference fringe between two object lights becomes large when the scattering angle of the light diffusion body becomes large. As mentioned above, when the efficiency of the "Fresnel noise" becomes large, the cloudiness of the hologram screen becomes large so that the it becomes the non-transparent state. Accordingly, it is necessary to change the intensity ratio ER/EO in order to decrease the efficiency of the "Fresnel noise".
As mentioned above, by changing the intensity ratio ER/EO in accordance with a size of the scattering angle of the light diffusion body, it is possible to increase the efficiency ηRO and to decrease the efficiency of the "Fresnel noise". In the hologram screen in which the efficiency ηRO is higher and the efficiency of the "Fresnel noise" is lower, the incident light to the hologram screen is not scattered so that it is possible to irradiate the output light with high efficiency. That is, it is possible to easily produce the hologram screen having the haze ratio of 5 to 60%.
When the haze ratio is 5 to 60%, it is possible to irradiate the image light with high efficiency. In this case, the scattering extent of the light, which is input from other light sources except for the image projector to the hologram screen, becomes low. Accordingly, when the observer observes the hologram screen, the cloudiness of the hologram screen due to the external light is small, the light from the back of the hologram screen is transmitted without cloudiness, and can reach the observer. Accordingly, the observer can clearly observe the back through the hologram screen. That is, according to the fourth aspect of the present invention, it is possible to produce the transparent hologram screen without cloudiness.
In the exposure optical system, as a method for changing the scattering angle of the light diffusion body, there are two methods, i.e., a method for exchanging the light diffusion body, and a method for using the light diffusion body integrated by laminating a plurality of light scattering bodies each having the same scattering angle or each having different scattering angle.
Further, the intensity ratio EO/ER by suitably changing the intensities EO and ER. For example, it is possible to adjust the change of the intensities EO and ER by suitably changing the reflection factor of each mirror and magnification of the object lens. In particular, it is preferable to change the reflection factor of the half-mirror since it is possible to avoid loss of the laser light.
In the producing method in this embodiment, it is possible to utilize a photopolymer and dichromated gelatin as the photosensitive material. However, there is the following problem. That is, since it is necessary to provide a wet type development process in the producing process using the dichromated gelatin, there is a problem in which cracks occur on the photosensitive material during producing process so that cloudiness occurs on the hologram screen. In the present invention, however, it is possible to provide the hologram screen without cloudiness by using various photosensitive materials, and to obtain the transparent hologram screen.
According to the invention, when enlarging the scattering angle of the light diffusion body, it is preferable to reduce the above intensity ratio ER/EO. As a result, it is possible to obtain the hologram screen without cloudiness since the haze ratio becomes 5 to 60% or less.
Further, it is possible to obtain the diffusion light having broad extent by enlarging the scattering angle of the light diffusion body, and to also obtain the hologram screen having broad view field by using the diffusion light as the object light. In the hologram screen having broad view field, since the image can be observed without a narrow limitation of the observer position, this hologram screen can be utilized without limitation in the place in actual use.
The embodiment will be explained with reference to
As shown in
In this embodiment, the hologram screen 41 is the transmission type, and a method of producing the hologram screen was explained in the second embodiment. On the other hand, as shown in
Next, in the hologram screen according to the embodiment, an evaluation test was performed regarding the relationship between the haze ratio and the cloudiness which was observed by the observer as follows. That is, in an environment shown in
As a method for obtaining the hologram screen having different haze ratio which was used in this evaluation test, the method for producing the hologram screen shown in the embodiment was utilized. That is, the intensity ratio ER/EO of the reference light and the object light is changed in accordance with the scattering angle of the light diffusion body in the exposure optical system shown in FIG. 88. One hologram screen was formed by laminating a plurality of hologram screens in order to obtain the desired haze ratio.
The hologram screen 41 used in the evaluation test has the width across corners of 20 inches. The horizontal illuminance of the light from the lamp 423 was 1000 (lux), and the brightness on the wall 421 which becomes the background of the hologram screen 41 was 400 (cd/m2). Further, the distance between the wall 421 and hologram screen 41 was 5 m, and the illuminance at the side of the observer 48 was 1000 (lux). Since the average illuminance is 500 (lux) in an office room, and a small shop, such as a convenience store, is 700 (lux), the brightness of the lamp 423 was set to 1000 (lux).
The visual recognition of the back of the hologram screen 41 was evaluated by the following test. That is, Gothic black characters including Chinese characters and alphabet, and each having a size of 36-point, were drawn on a white paper. This white paper was mounted on the wall 421 as the background of the hologram screen and as the exhibition 4210. This exhibition 4210, which is not irradiated by the image projector 412, was observed by the observer 48 who positioned apart from the hologram screen 41 by two meters. Then, the state of the characters (i.e., whether it is easy for the observer to read characters on the white paper) and the cloudiness extent of the back due to the hologram screen, were subjectively evaluated by the observers.
The result of the evaluation is shown in
On the other hand, in
As shown in
The method for producing the hologram screen is explained with reference to
In
In this case, there is the relationship of L/S=3/2 between the distance L (i.e., a length of light diffusion body 432) and the distance S (i.e., a distance between the light diffusion body 432 and the photosensitive material 431). Further, the photopolymer made by Dupont Co., Ltd. having the thickness of 6 μm was used as the photosensitive material 431, and the double-faced ground glass having the surface roughness of #1000 was used as the light diffusion body 432.
As mentioned above, the object light 4320 and the reference light 4310 are irradiated onto the photosensitive material 431 in order to record the interference fringe thereon. An amount of the exposure on the photosensitive material 431 was 30 mJ/cm2. After completion of the interference fringe, the ultraviolet was irradiated on the photosensitive material 431 with the intensity of 0.1 mJ/cm2, and the photosensitive material 431 was heated by temperature 120°C C. during two hours, so that the hologram screen was obtained.
Since the photosensitive material 431 is formed by a thin film, when it is used as the hologram screen, the thin film is supported by a transparent plate which is bonded thereto. Various performances of the above hologram screen were evaluated by the following test. In this test, the light diffusion body was formed by four kinds of light diffusion bodies each having different angle as shown in FIG. 89. The haze ratio of each hologram screen was measured as shown in FIG. 90. As shown in
Further, the relationship between the haze ratio and the intensity ER/EO due to the "Fresnel noise" formed by the interference fringe between two object lights, was checked as follows. That is, in the exposure optical system 43 shown in
As shown in
Further, as is obvious from comparison of the graph of
Accordingly, when producing the hologram screen having relatively high haze ratio, if the haze ratio due to the "Fresnel noise" is checked as shown in
As shown in
On the other hand, as shown in
When the hologram screen is produced based on the above processes, it is possible to reduce the haze ratio due to the "Fresnel noise" until the grade in which there is no influence for cloudiness of the hologram screen. Further, it is possible to reduce the haze ratio due to the normal interference fringe until the grade in which the transparency of the hologram screen can be ensured.
Next, in the exposure optical system shown in
Further, the relationship between the diffraction efficiency ηRO Of the normal interference fringe at the hologram screen, which was produced by using the light diffusion body of the scattering angle of 36°C, and the intensity ER/EO at the exposure, as shown in FIG. 95. In the measurement of the diffraction efficiency ηRO, as shown in
As shown in
Further, the intensity ER/EO is obtained for each light diffusion body shown in
As shown in
As is obvious from the above explanations, in the case that the brightness of the image is not always necessary, i.e., the efficiency of the hologram screen is not always required based on an environmental conditions using the hologram screen, it is possible to produce the hologram screen having good transparency by reducing the diffraction efficiency ηRO of the hologram screen.
Further, in the change of the scattering angle of the light diffusion body 432, the scattering angle is adjusted in such a way that, the larger the scattering angle, the smaller the intensity ratio ER/EO, when changing the intensity ratio ER/EO. As a result, it is possible to clearly observe the back through the hologram screen, and to produce the hologram screen having no cloudiness and good transparency. Further, when the screen gain is 0.3 or more, it is possible to produce the hologram screen which can clearly recognize the image.
Even if the exposure conditions is set as the diffraction efficiency ηROof the normal interference fringe of the hologram screen is constant, there is the case in which the haze ratio becomes low in accordance with increase of the efficiency of the "Fresnel noise". For example, in the production of the hologram screen based on the conditions in which the scattering angle of the light diffusion body is 36°C and intensity ratio ER/EO is 3, as shown in
Further, it is possible to change the haze ratio in accordance with the thickness of the photosensitive material when producing the hologram screen. The change of the haze ratio is shown in
As shown in
Takada, Kenichiro, Shiozawa, Masahiro
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